For the majority of drivers/owners, the choice of RWD or 4Matic hinges on the climate where the car will be driven.
Living in the NE of the US, there are 4WD/AWD cars and trucks of all brands everywhere because of the snowy winters. Although it doesn't address your question on reliability, I take a slightly different stance on choosing the wheels that do the driving, and my position echos some of Kajtek1's comments.
I've been driving for over half a century, grew up with only RWD, and prefer that type of handling to either FWD or alternatives like 4Matic.
When I decided to get my 212, I went to 5 local (within 100 miles) dealers looking for a NON-4Matic. Each dealer told me I would have to order a car because their 212 inventories, and inventories throughout the NE, were all 4Matic due to the preference of perspective owners.
My solution was to search the internet for a RWD 212 that also had all the other goodies that I wanted. I found exactly what I wanted in North Carolina, flew down there to buy it, and drove it home. That's what I think of 4Matic, but I understand it doesn't really help with your question about reliability.
So I guess the real question you should be asking yourself is whether you really need or would prefer a 4Matic for some reason. Good luck.